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United States Patent |
5,217,804
|
James
,   et al.
|
June 8, 1993
|
Magnetic particles
Abstract
Magnetic particles are cobalt surface treated gamma iron oxide (Fe.sub.2
O.sub.3) having a specific area of at least 30 m.sup.2 /g and a powder
coercivity greater than about 450 Oe, the particles being coated with from
about 10 to about 50% by weight of a material having a refractive index
less than about the refractive index of a binder for the particles.
Inventors:
|
James; Robert O. (Rochester, NY);
Bertucci; Sidney J. (Rochester, NY);
Oltean; George L. (Rochester, NY)
|
Assignee:
|
Eastman Kodak Company (Rochester, NY)
|
Appl. No.:
|
609673 |
Filed:
|
November 6, 1990 |
Current U.S. Class: |
428/329; 252/62.54; 252/62.56; 252/62.59; 252/62.63; 252/62.64; 428/403; 428/404; 428/407; 428/412; 428/421; 428/422; 428/425.1; 428/425.5; 428/425.9; 428/480; 428/483; 428/510; 428/532; 428/842.6 |
Intern'l Class: |
B32B 005/16; B32B 015/02; B32B 019/02; B32B 021/02 |
Field of Search: |
428/403,404,407,329,425.9,694,412,421,422,425.1,425.5,480,483,532,510
252/62.54,62.56,62.59,62.63,62.64
|
References Cited
U.S. Patent Documents
3782947 | Jan., 1974 | Krall | 96/67.
|
4279945 | Jul., 1981 | Audran et al. | 427/130.
|
4280918 | Jul., 1981 | Homola et al. | 252/62.
|
4302523 | Nov., 1981 | Audran et al. | 430/140.
|
4321303 | Mar., 1982 | Morita et al. | 252/62.
|
4336310 | Jun., 1982 | Okuyama et al. | 428/447.
|
4438156 | Mar., 1984 | Homola et al. | 252/62.
|
4874668 | Oct., 1989 | Asada et al. | 428/404.
|
4956220 | Sep., 1990 | Sueyoshi et al. | 428/328.
|
4990276 | Feb., 1991 | Bishop et al. | 252/62.
|
Foreign Patent Documents |
686172 | May., 1964 | CA.
| |
83207 | Jun., 1980 | JP | 252/62.
|
83209 | Jun., 1980 | JP | 252/62.
|
164706 | Sep., 1983 | JP | 428/404.
|
216510 | Oct., 1985 | JP | 252/62.
|
Primary Examiner: Thibodeau; Paul J.
Assistant Examiner: Nakarani; D. S.
Attorney, Agent or Firm: Gerlach; Robert A.
Claims
What is claimed is:
1. Magnetic particles in a binder to form a transparent magnetic layer
comprising a cobalt surface treated gamma iron oxide core having a
specific surface area of at least 30 m.sup.2 /g and exhibiting a powder
coercivity of greater than 450 Oe, the core surrounded by a shell, the
shell comprising from 10 to 50 percent by weight of the total weight of
the particle and being of a material having a refractive index less than
the refractive index of the binder.
2. The particles of claim 1 wherein the specific surface area of the core
is at least 40 m.sup.2 /g.
3. The particles of claim 1 wherein the powder coercivity of the core is
from about 650 to about 850 Oe.
4. The particles of claim 1 wherein the shell comprises from about 20 to
about 45 percent by weight of the particle.
5. The particles of claim 1 wherein the shell material is selected from the
group consisting of silica, magnesium fluoride, calcium, fluoride and
fluorinated hydrocarbon resins.
6. The particles of claim 5 wherein the shell material is silica.
7. The particles of claim 5 wherein the shell material is a fluorinated
hydrocarbon resin.
8. The particles of claim 7 wherein the shell material is
polytetrafluoroethylene.
9. The particles of claim 1 wherein the shell material contains voids.
10. The particles of claim 1 wherein the refractive indices of the shell
and the binder are less than the refractive index of the core.
11. Magnetic particles comprising a cobalt surface treated gamma iron oxide
core having a specific surface area of at least 30 m.sup.2 /g and
exhibiting a powder coercivity of greater than 450 Oe, the core surrounded
by a shell, the shell comprising from 10 to 50 percent by weight of the
total weight of the particles of a material selected from the group
consisting of silica, magnesium fluoride, calcium fluoride and fluorinated
hydrocarbon resins.
12. The particles of claim 1 wherein the binder is gelatin, a cellulose
ester, a polyurethane, a polyester or a polycarbonate.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to magnetic particles and particularly to magnetic
particles having a coating thereon suitable for use in a magnetic
recording layer particularly on a photographic element the magnetic
recording layer being transparent in a photographic sense.
2. Description of Related Art
Conventional magnetic recording elements that are used for recording sounds
or images are generally opaque to visible light regardless of the nature
of the magnetic particles used in such elements. For example, motion
picture films often are provided with a magnetic sound track which
generally is opaque and does not cover that portion of the film used in
the projection of images.
U.S. Pat. No. 4,280,918 discloses magnetic particles provided with a
uniform coating of colloidal silica to prevent the aggregation of the
magnetic particles in the magnetic coating mixture.
U.S. Pat. No. 4,336,310 discloses a substrate coated with a magnetic layer
comprising a binder resin and a metallic magnetic powder supporting silica
on the surface coated with sequential layers of hydrolyzed silane compound
and oleic acid.
Canadian Patent 686,172 shows that a magnetic recording layer may be
transparent to visible light when it contains low concentrations of
magnetizable particles. According to this patent, such a layer is coated
over a layer containing descriptive material which allows a user to
simultaneously hear and see certain subject matter. However, this patent
points out that the electromagnetic characteristics, i.e., the magnetic
recording and reproducing characteristics, of such a layer are inferior to
those of conventional magnetic layers as a result of the very low
concentration of magnetizable particles.
U.S. Pat. No. 3,782,947 discloses a photographic product which carries
magnetic particles distributed across the image area of the product. The
particle distribution and sizes are so designed that the composite
granularities of the photographic and magnetic distribution is essentially
transparent in a photographic sense. According to this patent, the
photographic image can be viewed via the magnetic distribution and the
magnetic distribution can be employed for recording and playback
information.
U.S. Pat. No. 4,279,945 and 4,302,523 disclose a process of preparing
magnetic recording elements containing a transparent recording layer.
According to these patents, the magnetic recording and reproducing
characteristics obtained are comparable to conventional opaque magnetic
layers without the need for matching the granularity of a magnetic medium
to that of a photographic medium. However, the process requires that the
layer containing magnetic particles be treated using one or both of the
following process steps, (1) compacting the layer while it is in a
malleable state to reduce its thickness (e.g., calendaring), or (2)
imbibing into the layer a substantially transparent liquid having a
refractive index that is substantially the same as that of the binder.
Elements of the type described in the above-cited patents have not achieved
widespread commercial success for various reasons. For example, the
elements described in U.S. Pat. No. 4,279,945, as indicated by the Figure
therein, are substantially opaque at wavelengths less than about 500 nm
and thus are not useful in color films. Further, the disclosed process
requires that the magnetic recording layer be calendered while it is in a
malleable state and/or that a transparent liquid be imbibed into the
magnetic recording layer.
It is evident that it would be highly desirable to provide magnetic
particles that when incorporated into a transparent binder will provide a
layer of film that is transparent in the photographic sense but also
capable as a magnetic recording layer exhibiting improved magnetic and
photographic performance. This goal is difficult to achieve because of the
nature of the magnetic particles and the concentration of particles
required to provide a sufficient signal to write and read magnetically
stored data. There may also be noticeable color and haze associated with
the magnetic layer depending upon the type of pigment, the concentration
of the pigment and the effective particle size thereof.
The critical photographic properties affected by the magnetic layer are the
optical density and the granularity. To reduce the impact of the magnetic
layer on photographic quality, both the optical density and the
granularity must be minimized so these properties have no adverse effects
on the color, the brightness of highlighted areas and the granularity of
prints made from negatives or projected images from transparencies. This
is what is meant when layers are spoken of herein as being "transparent in
a photographic sense".
In co-pending application Ser. No. 473,494, filed Feb. 1, 1990 by Robert O.
James and John Rieth, and entitled "Photographic Element Containing Thin
Transparent Magnetic Recording Layer and Method For the Preparation
Thereof" is disclosed and claimed photographic elements containing a
transparent magnetic recording layer wherein the magnetic particles
included in the recording layer are cobalt surface treated gamma iron
oxide particles having a specific surface area of at least 30 m.sup.2 /g
in a concentration of the magnetic particles being from about 10 to about
1000 milligrams/m.sup.2.
SUMMARY OF THE INVENTION
This invention provides new and improved magnetic particles for
incorporation into transparent magnetic layers the magnetic particles
containing cobalt treated gamma iron oxide having a specific surface area
of at least 30 m.sup.2 /g and exhibit powder coercivities greater than 450
Oe, the magnetic particles being coated with from about 10 to about 50% by
weight of a material having a refractive index less than the refractive
index of the binder material into which the magnetic particles of this
invention are to be incorporated.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1a is a diagrammatic representation of a magnetic core particle having
a uniform coating thereon with a portion cut away for purposes of
understanding;
FIG. 1b is a similar view of a magnetic core particle where the coating is
particulate in nature;
FIG. 2 is a graph which plots optical density against wavelength
illustrating the improved transparency of two compositions in accordance
with this invention in comparison to a control sample.
FIG. 3 is a graph plotting optical density against laydown for the same
three samples as shown in FIG. 2 at a wavelength of 450 nanometers;
FIG. 4 is a graph similar to FIG. 3 with the exception that the wavelength
is 550 nanometers.
FIG. 5 is a graph similar to FIG. 2 plotting optical density against
wavelength for two different compositions in accordance with this
invention in comparison with a control sample.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
As indicated previously the invention relates to magnetic particles
suitable for incorporation into transparent layers which layers are
capable of having coded information written and read therefrom. The
transparent layers containing the magnetic particles in accordance with
this invention are particularly applicable for use in combination with
photographic films wherein information can be written into the magnetic
layer without affecting the quality and performance of the light-sensitive
photographic elements. In order to achieve this result it is necessary
that a sufficient quantity of a particular type of magnetic particle be
incorporated into a transparent binder as described and claimed in
copending application Ser. No. 609,672, filed Nov. 6, 1990 and entitled
"Transparent Magnetic Recording Layers And Photographic Elements
Containing The Same", incorporated herein by reference. The magnetic
particles in accordance with this invention, exhibit a decreased light
extinction cross-section in comparison with uncoated particles.
Referring specifically to FIGS. 1a and 1b, 1a illustrates a magnetic
particle 11 having a core 13 coated with a shell 15. The shell 15 is cut
away in order to better illustrate the nature of the particles. The shell
of FIG. 1a is uniform in nature and forms a continuous coating on core 13.
The shell 15' in FIG. 1b is not a uniform layer but is particulate in
nature. The necessary characteristics of the magnetic particles in
accordance with this invention are (1) the magnetic core must have a
specific area of at least 30 m.sup.2 /g; (2) the core is a cobalt surface
treated gamma iron oxide (Co-.gamma.-Fe.sub.2 O.sub.3) having a powder
coercivity of at least 450 Oe and preferably from about 650 to about 850
Oe; (3) the shell material must have a refractive index less than that of
the binder in which the particles are to be incorported, and (4) the shell
material must comprise at least 10% by weight of the entire particle,
preferably from about 15% by weight to about 50% by weight. Regarding (3)
above, the refractive indices of the shell and the binder are less than
the refractive index of the magnetic core particles, however, as a
practical matter this is generally the case as the refractive index of the
core is generally from about 2.5 to 3.
These requirements with regard to the particulate magnetic material, when
incorporated into a transparent layer in the proper concentration insures
that the magnetic layer is substantially transparent in photographic
sense, while at the same time the presence of the magnetic material is
sufficient to provide a signal to write and read magnetically stored data.
The critical photographic properties affected by the magnetic layer as
indicated are the optical density and the granularity. To reduce the
impact of the magnetic layer on a photographic layer of a light-sensitive
element, when the magnetic layer extends over the face of the
light-sensitive element, both the optical density and the granularity must
be minimized so that these properties have no affect on the color, the
brightness of highlight areas and the granularity of prints made from
negatives or projected images from transparencies.
Cobalt surface treated gamma iron oxide particles having the necessary
specific surface areas of at least 30 m.sup.2 /g and exhibiting the powder
coercivities indicated above are commercially available and can be
obtained from Toda Kogyo Corporation under the trade designations CSF
4085V2 CSF 4565V, CSF 4585V and CND 865V. Further, pigments supplied by
Harcros Pigment Inc. under the trade designations RPX-4392, RPX-5003,
RPX-5026 and RPX-5012 are suitable as starting materials for the
preparation of the coated particulate magnetic materials in accordance
with this invention.
Regarding the value of the refractive index of the shell material expressed
as less than the refractive index of the binder materials in which the
particles are dispersed, as a practical matter most binder materials have
a refractive index greater than 1.5. Therefore, to achieve the
transparency in a photographic sense, a refractive index of the shell
material less than 1.5 is generally satisfactory. For example, the
refractive indices of cellulose acetate varies from 1.46-1.5 and gelatin
is about 1.5. Any shell material having a refractive index less than the
refractive index of the binder is suitable. However, it will be
appreciated that the greater the difference between the refractive index
of the shell and the binder, the greater is the possible reduction in the
light extinction efficiency. Any suitable material capable of being coated
on the particulate material having a refractive index less than that of
the binder material employed in the preparation of a magnetic layer may be
used as the coating on the particulate cobalt treated gamma iron oxides
such as for example, magnesium fluoride, calcium fluoride, halogenated
hydrocarbon such as polytetrafluoroethylene, polyhexafluoropropane,
polyvinylidene fluoride, and the like, silica, composite materials of
silica and alumina, and the like. Voids may be included within the shell
material to effectively lower the refractive index of the shell. In this
manner, materials normally not suited for the shell, because the
refractive index is higher than that of the binder may be employed, so
long as the refractive index is lowered due to the presence of the voids,
to less than that of the binder. Suitable materials for the shell together
with their refractive indices are set forth in Lange's Handbook of
Chemistry, Eight Edition, Published by Handbook Publishers, Inc., 1952, at
pages 1259-1306. As illustrated with respect to FIGS. 1a and 1b, the
coating on the particulate magnetic particle may be a uniform coating or
may itself be particulate and may contain voids as expressed above.
The coated cobalt treated gamma iron oxide particles of this invention may
be prepared by any suitable technique whereby thick coatings as required
by this invention can be applied to the core material such as by the
precipitation of soluble silicates to form skins of dense hydrated
amorphous silica as disclosed in U.S. Pat. No. 2,885,366. While "thick" as
used above is a relative term, the thickness dimension of the shell
generally varies from about 10 nm to about 200 nm. The optimum thickness
of the shell depends on the volume of the core particles. In order to coat
the magnetic particles having the requisite specific surface area and
coercivity in accordance with this invention, it is generally first
necessary to wet the magnetic particles as received from the manufacturer
in order to deaggregate and disperse the particles. This is generally
achieved by employing various wetting agents or dispersants in aqueous
dispersions containing the dispersed particles. Milling is conducted in
order to deaggregate the particles. A dense silica skin can be
precipitated onto the particles by the addition of sodium silicate and
sulfuric acid.
Other silica coatings can be formed on the magnetic core by dispersing the
magnetic particles in aqueous solutions using an alkaline wetting agent.
This results in a negative charge on the particle surface which is
reversed to a positive charge by a heterocoagulation or adhesion of
particles of an alumina sol. This positively charged magnetic composite
can then be coated with a negatively charged particulate colloidal silica
to yield a composite magnetic oxide/alumina/silica particle having a shell
containing about 30% by weight. The weight percentage of the shell
material can then even be further increased by coating with a dense form
of silica as illustrated in a subsequent example to provide a particle
having a shell wherein the shell is approximately 42% by weight.
Other methods of preparing a core shell structure may also be employed. For
example, silica shells can be grown on magnetic iron oxide cores by a
modified sol gel process. In this process silicon tetraalkoxide dissolved
in anhydrous alcohol is added to an alcoholic dispersion of the cobalt
gamma iron oxide particle and then hydrolyzed by the addition of an
ammonia solution to yield the particles having a silica shell surrounding
the magnetic cobalt gamma oxide core.
Fluorocarbon coated cobalt treated gamma iron oxide particles can be made
by a procedure analogous to that described in an article entitled
"Interactions in Mixed Fluorocarbon Latex-Hematite Dispersions" by M.
Visca, S. Savonelli, E. Barouch and E. Matijevic published in the Journal
of Colloid and Interface Science, Vol. 122, No. Apr. 2, 1988.
The coated magnetic particles in accordance with this invention are
employed in the fabrication of transparent magnetically recordable layers
or films having the above described magnetic properties and photographic
elements that include a support, a light-sensitive layer and a transparent
magnetic recording layer. Transparent magnetic recording layers or films
would have widespread application in many environments wherein it would be
desirable to include or encode information without interfering with the
visual appearance of the object onto which the magnetic recording is made.
For example, in a sheet of written text or a picture, information could be
recorded in a magnetic recording transparent layer without interfering
with the visual appearance of the text or the picture underlying the
transparent magnetic recording layer. Such transparent recording layers
can be prepared simply by incorporating the above described coated
magnetic particles in the correct concentration in a film forming binder
or by applying such a film forming binder to a substrate. For example, if
it were desired to provide magnetically encoded information to this page
of text, a layer of the above-described magnetic particles in a binder
could be either coated onto the page of text or a self-standing film
containing the appropriate concentration of magnetic particles could first
be prepared and then laminated to this printed page. This would then
enable one not only to read the visual text in the normal manner but also
to read out the information contained in the encoded magnetic transparent
layer.
The primary utility for transparent magnetic recording layers is in the
photographic industry wherein a photographic film can be built onto a
substrate that includes a transparent recording layer. The transparent
magnetic recording layer may be disposed in any position relative to the
various layers of the photographic film including over the light sensitive
layers, within the layers, within the base substrate, however, it is
preferred that the transparent magnetic layer be applied as a layer on the
side opposite the light-sensitive layers of the photographic film. This
provides ease of encoding and readout. One suitable technique would be to
prepare the substrate for the film whether it be cellulose acetate,
polyethylene terephthalate, polycarbonate paper or other suitable
substrate for that purpose with a transparent magnetic recording layer on
one surface thereof. This again can be achieved either by coating
applications widely known in both the photographic and magnetic recording
fields of technology or by forming a self-sustaining film of the
above-described magnetic particles in a transparent binder and laminating
this to the photographic substrate. Information can then be encoded into
the magnetic layer during all steps of the preparation of the photographic
product. This can include manufacturing data with regard to the various
layers that are employed during the preparation of the film, information
with regard to the properties of the various layers built onto the
substrate and the like. Further, after the film is completed and is being
used by the consumer, many and various applications can be envisioned
wherein information is included in the magnetic layer that is helpful to
the photographer, the developing laboratory and others engaged in this
field of endeavor. For example, which a camera also has the capability of
imparting data to a magnetic layer by having built in recording heads into
the camera, information with regard to each frame of the film can be
recorded, such as, the light conditions, the speed at which the frame is
exposed, the F-Stop number and the like.
The support film and transparent magnetic recording layer preferably are
provided in the form of a composite unitary structure consisting of at
least the flexible support film and the substantially transparent magnetic
recording layer prepared in a process as described in co-pending
application Ser. No. 473,494, filed Feb. 1, 1990, to R. O. James and J.
Rieth, which is incorporated herein in its entirety. Preferably to have
nearly isotropic magnetic and optical properties of the film, care should
be taken to randomly arrange the anisotropic particles in the binder. It
may be desirable to perpendicularly orient the magnetic particles. This
may be accomplished utilizing the teaching of U.S. Pat. No. 4,859,495
issued Aug. 22, 1989 to James P. Peng (incorporated herein by reference).
In forming the transparent magnetic recording layer, the above-described
magnetic particles are homogeneously dispersed in a substantially
transparent binder and a solvent for the binder. Any suitable transparent
binder may be employed including cellulose organic acid esters, such as,
for example, cellulose diacetate, cellulose triacetate, cellulose acetate
butyrate, cellulose nitrate, cellulose acetate propionate and the like;
polyurethanes, polyesters, polycarbonates and the like. Suitable solvents
include methylene chloride, methyl alcohol, methyl ethyl ketone, methyl
isobutyl ketone, ethyl acetate, butyl acetate, cyclohexanone, butyl
alcohol, dimethylformamide and the like as well as mixtures thereof. The
dispersing medium can also contain transparent addenda, for example,
plasticizers such as tricresyl phosphate, dibutyl phthalate or dioctyl
phthalate; lubricants such as carbonic acid mixed esters such as ethyl
cetyl phosphate, stripping acids, and the like.
In preferred embodiments of the invention, a dispersing or wetting agent is
added to facilitate dispersion of the magnetic particles. Useful
dispersing agents include a fatty acid amine, and commercially available
wetting agents or surfactants such as Emcol CC59 which is quaternary amine
available from Witco Chemical Corp., Gafac PE 510, Gafac RE 610, Gafac RE
960, and Gafac LO 529 which are phosphoric acid esters available from GAF
Corp. The dispersion can be formed by diluting a concentrate of the
magnetic particles and optionally a wetting agent dispersed in dibutyl
phthalate with a solvent solution including the binder. Details of a
preferred dispersion preparation and dilution procedure are set forth in
U.S. patent application Ser. No. 473,500, filed Feb. 1, 1990, the
disclosure of which is hereby incorporated by reference in its entirety.
The element of the invention includes a support film for color or black and
white negative or reversal film applications which preferably is
substantially transparent. Any of the support materials listed above or
disclosed in Paragraph XVII of Research Disclosure 308119 Issue Number 30,
December 1989 may be used. The support film can be cast according to
methods known in the art from a dope including one or more of the
above-described support materials and a solvent such as methylene chloride
or any other solvent selected from those described above or mixtures
thereof. The support film dope can include any of the conventional addenda
known in the art to be useful therein including the transparent
plasticizers discussed above, stripping acids, and so forth.
In an alternative embodiment to that disclosed in copending application
Ser. No. 473,494, mentioned above, the magnetic particles dispersed in a
suitable binder may be applied to a suitable support by any of the
conventional coating techniques known in the art to achieve the required
coverage and thus the necessary concentration in the magnetic layer to
thereby provide a recordable layer while at the same time being
transparent in a photographic sense.
Photographic elements in accordance with this invention comprise at least
one photosensitive layer. Such photosensitive layers can be image-forming
layers containing photographic silver halides such as silver chloride,
silver bromide, silver bromoiodide, silver chlorobromide and the like. Any
of the known silver halide emulsion layers, such as those described in
Research Disclosure, Vol. 176, December 1978 Item 17643 and Research
Disclosure Vol. 225, January 1983 Item 22534, the disclosures of which are
incorporated by reference in their entirety, are useful in preparing
photographic elements in accordance with this invention. Generally, the
photographic element is prepared by coating the support film on the side
opposite the magnetic recording layer with one or more layers comprising a
dispersion of silver halide crystals in an aqueous solution of gelatin and
optionally one or more subbing layers, such as, for example, gelatin, etc.
The coating process can be carried out on a continuously operating machine
wherein a single layer or a plurality of layers are applied to the
support. For multicolor elements, layers can be coated simultaneously on
the composite support film as described in U.S. Pat. No. 2,761,791 and
U.S. Pat. No. 3,508,947. Addition useful coating and drying procedures are
described in Research Disclosure, Vol. 176, December 1978, Item 17643.
Suitable photosensitive image forming layers are those which provide color
or black and white images.
As is taught in U.S. Pat. No. 3,782,947 noted above, whether an element is
useful for both photographic and magnetic recording depends on both the
size distribution and concentration of the magnetic particles and on the
relationship between the granularities of the magnetic and photographic
coatings. Generally, of course, the coarser the grain of the emulsion in
the photographic element that contains the magnetic recording layer, the
larger the mean size of the magnetic particles which can be tolerated. A
magnetic particle concentration between about 1 and 10 mg/1000 cm.sup.2
when uniformly distributed across the desired area of the photographic
element will be sufficiently photographically transparent. Particle
concentrations less than about 1 mg/1000 cm.sup.2 tend to be insufficient
for magnetic recording purposes and particle concentrations greater than
about 10 mg/1000 cm.sup.2 tend to be too dense for photographic purposes.
Particularly useful particle concentrations are in the range of 2-8
mg/1000 cm.sup.2. Concentrations of from about 4.5 mg/1000 cm.sup.2 to
about 5.5 mg/ 1000 cm.sup.2 have been found to be particularly useful in
reversal films.
The photographic elements according to this invention can contain one or
more conducting layers such as antistatic layers and/or anti-halation
layers such as described in Research Disclosure, Vol. 176, December 1978,
Item 17643 to prevent undesirable static discharges during manufacture,
exposure and processing of the photographic element. Antistatic layers
conventionally used in color films have been found to be satisfactory for
use herewith.
The invention will be further illustrated by the following examples:
EXAMPLE 1
Preparation of Coated Magnetic Particles
1 kg of Co-.gamma.-Fe.sub.2 O.sub.3 particles of surface area 45 m.sup.2 /g
and coercivity 650 Hc available from Toda Kogyo under the trade
designation CND865V2 were milled in 2 liters of 0.5M H.sub.2 SO.sub.4
using 2 mm glass beads. After milling the slurry was washed with water to
pH 4.5 and concentrated to 28% by weight solids. The coercivity of the
product powder was 465 Oe due to loss of cobalt from the surface. The
specific area was 44.2 m.sup.2 /g and the saturation magnetization was
72.4 emu/g.
A dense silica skin was preciptated onto the particles of this dispersion
by the simultaneous addition of a sodium silicate solution (solution A)
and sulfuric acid (solution B) as follows:
______________________________________
Solution A 198.04 g sodium silicate
(40% by weight as SiO.sub.2)
76.56 g sodium sulfate
6980 ml water
Solution B 29.6 g sulfuric acid
98.6 g sodium sulfate
6980 ml water
______________________________________
790.7 g of slurry (at 28% oxide) was diluted to 11.03 liters with water to
form a 2% dispersion in a 25 liter reactor.
The slurry was heated to 90.degree. C. Solutions A and B were preheated to
65.degree. C. and pumped simultaneously into the reactor at a rate of 200
ml/min. The pH was maintained between 9 and 10. After addition was
completed, the temperature was maintained at 94.degree. C. for 30 minutes
and allowed to cool for a further 30 minutes to 35.degree. C. The pH was
adjusted to pH 7.0 and slurry stood overnight, after which the particles
were recovered. Particle coercivity was 514 Oe, saturation magnetization
63.8 emu/g and the percent silica was 11.9% (Powder A).
EXAMPLE 2
A high surface area, (41 m.sup.2 /g) high powder coercivity (H.sub.c 850
Oe) Co-surface treated-.gamma.-iron oxide powder CSF4085V2 supplied by
Toda Kogyo Corp. was dispersed in an aqueous solution medium for 3 hours
using a small media mill. The formulation was as follows:
______________________________________
Co-.gamma.-Fe.sub.2 O.sub.3
600.0 g
Water 721.3
Dispersant (Dequest 2006, 40%
12.0
active solution sold by Monsanto
1333.3 g
______________________________________
Dequest 2006 is pentasodium amino tris(methylenephosphate). The surface
charge of these particles at pH 9.9 was determined by electroacoustic
methods to be negative.
This dispersion was then treated with an alumina sol sold by Nalco Chemical
Co. under the trade designation Nalco 1SJ-614 (particle size about 2 nm)
to reverse the particle charge to positive and to promote adhesion of
colloidal silica sol particles (about 20 nm diam) in the following manner.
1084 g of the above aqueous dispersion at 44% solids and 150 g of H.sub.2 O
were milled for 30 minutes in a small media mill. Over a period of 30
minutes 123.2 ml of a fine alumina sol, pH 5 containing 12.3 g Al.sub.2
O.sub.3 were added to the mill.
At this stage the composition of the slurry was:
______________________________________
Co-.gamma.-Fe.sub.2 O.sub.3
476.9 g
Al.sub.2 O.sub.3 12.3
Water 981.7
Dequest 2006, 40% solution
9.8
______________________________________
Reaction was allowed to continue for another 60 minutes. 300 g of distilled
water and 492 g of colloidal silica sol at 30% by weight silica containing
147.8 g SiO.sub.2 were added to the Al.sub.2 O.sub.3 -Co-surface
treated-.gamma.-Fe.sub.2 O.sub.3 during continued milling over a period of
30 minutes. Milling was continued for 30 minutes. A further 600 g of water
was added over a 30 minute period while milling was continued. The
dispersion was recovered from the mill. (Powder B)
Measurements of the saturation magnetization of the starting powder (72.5
EMU/g) and the composite coated product Powder B (51.0 EMU/g) indicates
that the shell was 29.7% of the total mass of the particles. The dried
powder had a specific surface area of 85.1 m.sup.2 /g by BET analysis of
N.sub.2 adsorption isotherms.
EXAMPLE 3
Thicker coatings of SiO.sub.2 can be achieved by adsorption of a dense
silica layer on the particulate SiO.sub.2 particles described in Example
2.
The following three compositions were prepared separately:
______________________________________
1. 2% By Weight Solid Particle Slurry
1097 g
Final Slurry from Example 2
with 26% solids, 18.6% Co-.gamma.-Fe.sub.2 O.sub.3
Water 13153
Sodium sulfate Na.sub.2 SO.sub.4
202.4
14452.4 g
2. Solution C
Sodium silicate 40% SiO.sub.2
51.0 g
Sodium sulphate Na.sub.2 SO.sub.4
39.4
Water 3596
3686.4 g
3. Solution D
Sulfuric acid H.sub.2 SO.sub.4
7.62 g
Sodium sulfate Na.sub.2 SO.sub.4
50.83
Water 3596
3653.45 g
______________________________________
The particle slurry was heated with stirring in a reactor to 90.degree. C.
The pH was adjusted from pH 6 to pH 9.4 with 50% sodium hydroxide
solution.
Solutions C and D were added simultaneously at a rate of 17 ml/min. over
3.5 hours. The slurry pH was periodically checked and small adjustments
were made to maintain pH between 9 and 10. After addition was completed
the reactor was held at 90.degree. C. for a further 15 minutes.
The slurry was cooled to 25.degree. C. and then the pH was adjusted to pH 7
with 0.5M H.sub.2 SO.sub.4. The coated oxide was washed until the
conductivity was less than 40 micro mho cm.sup.-1. Finally the aqueous
solution was separated from the particles and the sample was air dried
(Powder C). The saturation magnetization of this sample, Powder C, was
found to be 42.2 EMU/g and the shell was 41.8% of the mass of the
particles. The specific surface area was 88.9 m.sup.2 /g by BET analysis
of N.sub.2 adsorption.
EXAMPLES 4 (CONTROL), 5 AND 6
A coating dispersion was prepared in accordance with the following recipe.
The control, Example 4 used cobalt surface treated gamma iron oxide
(Co-.gamma.-Fe.sub.2 O.sub.3) having a specific surface area of 41 m.sup.2
/g. Examples 5 and 6 employed Powder B (Example 2) and Powder C (Example
3), respectively.
______________________________________
Magnetic Particles 385.0 g
Emcol CC59 13.5
available from Witco Chemical Co.
UCARMAG 528 5.0
available from Union Carbide Corp.
CA139 (Morthane polyurethane
83.3
binder)
available from Morton Thiokol, Inc.
Butylmyristate 3.9
Myristic acid 3.9
Tetrahydrofuran 355.6
Cyclohexanone 625.3
Each of the three concentrates was diluted as follows:
Concentrate 10 g
Binder CA139 100
Tetrahydrofuran 283
Cyclohexanone 607
1000 g
______________________________________
The three resulting diluted dispersions were each coated thinly on a
transparent Mylar substrate to give a dry down thickness of 1 to 3 .mu.m
and provide a magnetic pigment laydown of 1 to 10 mg/1000 sq cm.
Comparison of the optical density of the layer containing the coated powder
particles B Example 5) and C (Example 6) with a layer containing uncoated
Co-.gamma.-Fe.sub.2 O.sub.3 (Example Control 4) is shown in FIG. 2 as a
function of wavelength at lay down levels of 7.2 mg/ft.sup.2, 7.2
mg/ft.sup.2 and 7.8 mg/ft.sup.2 all as Fe.sub.2 O.sub.3, respectively.
For wavelengths longer than 400 nm the films with Powders B and C exhibit
lower optical densities than that of the control.
Comparisons of optical densities of Examples 4 (Control), 5 and 6 at two
wavelengths 450 nm and 550 nm are shown in FIGS. 3 and 4, respectively, as
a function of laydown magnetic component concentration in mg/ft.sup.2 as
Fe.sub.2 O.sub.3 (x 1.0764=mg/1000 cm.sup.2).
At 450 nm, the SiO.sub.2 coated Co-.gamma.-Fe.sub.2 O.sub.3 show increasing
advantages over Example 4 as laydown increases. At 550 nm the advantages
of Examples 5 and 6 are more significant. A consequence of the fine
dispersion and lower optical density is the reduction in the granularity
of these transparent layers.
EXAMPLE 7 (Control) 8, and 9
These three examples utilize the same magnetic particles as Examples 4
(Control), 5 (Powder B) and 6 (Powder C), respectively.
A concentrate was prepared for each of the three magnetic materials by
milling the following composition in a 250 cc small media mill using steel
milling media for 6 hours
______________________________________
Magnetic Particles 500 g
Wetting agent GAFAC PE510
25 g
available from GAF
Solvent: Dibutylphthalate
975 g
1500 g
______________________________________
Dispersions prepared above, are diluted with a cellulose triacetate
solution in methylene chloride and methyl alcohol in a high shear mixer to
yield the following casting composition:
______________________________________
Weight Percent
______________________________________
Methylene chloride 83
Methanol 6.175
Butanol 2.8
Cellulose triacetate 6.5
(binder)
Dibutyl phthalate 1%
(non-volatile solvent)
GAFAC PE510 0.025
(wetting agent)
Magnetic Particle 0.5
100.000%
______________________________________
This dispersion is coated on a cellulose acetate base such that the pigment
laydown expressed as mg Fe.sub.2 O.sub.3 /1000 cm.sup.2 to form thin
(about 1 .mu.m) layers of cellulose acetate containing uniformly dispersed
magnetic particles. At these levels of pigment coded information can be
written and read from the magnetic layers by use of suitable
write/playback heads.
In addition to the magnetic pigments various dyes including magenta and
blue may also be formulated in the pigmented layer to give neutral density
films for the purpose of making reversal (color slide) films.
Another function of the magenta pigment and the dyes is the reduction of
light piping from the exposed ends, sides or perforations in the film.
A comparison of optical density of each of the three layers is shown in
FIG. 5 wherein optical density is plotted against wavelength for each of
Examples 7 (Control), 8 and 9 coated at laydown levels of 4.1 mg/ft.sup.2,
4.4 mg/ft.sup.2 and 4.3 mg/ft.sup.2 all as Fe.sub.2 O.sub.3, respectively.
Further, in a similar fashion to that shown in FIGS. 2 and 4, as the
laydown increases the decrease in optical density of the particles in
accordance with this invention becomes greater.
It is to be understood that other materials can be employed in the examples
for the shell materials of the magnetic particles, the binder materials
and the substrates so long as the necessary limitation set forth above are
met.
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